As a method of switching wireless network media from one to another smoothly between different wireless network media such as a mobile phone network, a WiMAX network, or the like, while maintaining a communication session between a mobile terminal and the wireless network media, a method using a mobile IP system has been considered.
In the mobile IP system, for the communication performed between a mobile terminal and a partner terminal, a home agent which manages an address of the mobile terminal being at a visited location forwards a communication data transmitted from the partner terminal to a mobile terminal at the visited location. With this, it becomes possible to search out an optimal network for communication at a specific time and a specific location for the mobile terminal and switch a connecting destination in a flexible manner.
For example, a user of a mobile terminal which corresponds to the above described mobile IP system can use a communication service by switching carriers and different types of networks (wireless network media) seamlessly in such a manner as being connected to a wireless LAN when the user is in an office; being automatically connected to a broadband connecting service such as the WiMAX network and the mobile phone network when the user is out of the office; and being automatically connected to a relatively slow mobile phone connecting service when the user is out of town.
A traditional mobile IP control system includes: a mobile terminal 50 which is connectable to different wireless network media; a home network 512 which is set in advance to be a network to which the mobile terminal 50 belongs; a home agent 520 which configures a part of the home network 512 and, at the same time, is connected to an IP network 11 being a public network; and a mobile phone network 513, a wireless LAN network 514, a WiMAX network 515, and a VPN network 516 which are connected to the IP network 11 respectively. The traditional mobile IP control system is configured such that a partner terminal 60 which executes a mutual communication with the mobile terminal 50 via the home agent 520 is connected to the IP network 11.
There, the mobile phone network 513 includes a radio base station 540A which presents a radio link to the mobile terminal 50 and a foreign agent 530A which relays a mutual communication performed between the radio base station 540A and the home agent 520, where the mobile phone network 513 is connected to the IP network 11 via the foreign agent 530A.
Also, the wireless LAN network 514 includes an access router 540B which presents a radio link to the mobile terminal 50 and a foreign agent 530A which relays a mutual communication performed between the access router 540B and the home agent 520, where the wireless LAN network 514 is connected to the IP network 11 via the foreign agent 530A.
Further, the WiMAX network 515 includes a radio base station 540C which presents a radio link to the mobile terminal 50 and a foreign agent 530C which relays a mutual communication performed between the radio base station 540C and the home agent 520, where the WiMAX network 515 is connected to the IP network 11 via the foreign agent 530C.
Also, the VPN network 516 includes a radio base station 540D which presents a radio link to the mobile terminal 50 and a foreign agent 530D which relays a mutual communication performed between the radio base station 540D and the home agent 520, where the VPN network 516 is connected to the IP network 11 via the foreign agent 530D.
Here, a method used in the traditional mobile IP control system for the communication from the partner terminal to the mobile terminal will be described.
First, a network (home network) to which the mobile terminal 50 belongs and a unique address (home address) which is not changed by movement of the mobile terminal 50 are set in advance for the mobile terminal 50.
The mobile terminal 50 acquires a foreign address (hereinafter referred to as “care-of address”) corresponding to an address system of each network, by establishing a radio connection with a network other than the home network, i.e., the mobile phone network 513, the wireless LAN network 514, the WiMAX network 515, or the VPN network 516 here.
The mobile terminal 50 notifies the home agent 520 of an acquired care-of address. The home agent 520 registers the care-of address so as to be associated with the home address of the mobile terminal 50.
Meanwhile, in the mobile IP control system, all the packets transmitted from the partner terminal 60 to the mobile terminal 50 are sent into the home agent 520. There, the home agent 520 adds the notified care-of address to the packets which are sent to the home address of the mobile terminal 50, and forwards the packets to the mobile terminal 50. The forwarded packets are received by the foreign agent, and the added care-of address is removed. Then, the packets are forwarded to the mobile terminal 50.
In each network medium of the mobile phone network 513, the wireless LAN network 514, the WiMAX network 515, and the VPN network 516, radio communication is performed with the mobile terminal 50 with which a radio connection is established, by using each different communication band.
Therefore, when the mobile terminal 50 performs a handover between the above described different network media, a delay or a data loss can be generated to the packet sent to the mobile terminal 50. This is attributed to the fact that the radio communication band used for the radio connection is different between a network media from which the connection is switched and another network media to which the connection is switched.
Also, as data transmitted/received via the IP network, the communication data which requires a relatively large communication capacity, such as audio data for an IP phone and the video and music data distributed by streaming, has become more common recently. Since the communication transmitting and receiving the above described communication data is performed in a real-time manner, a communication delay and a data loss result in interruption of the audio and distortion of the video image. Therefore, the communication delay and the data loss described above become major factors in disturbing the communication system itself.
Consequently, the necessity to control a communication quality (QoS: Quality of Service) by managing the radio communication band used in the mobile IP control system, for effectively using the radio communication band, is arisen.
For example, a method of providing an information control service corresponding to the care-of address at a visited location of the mobile terminal is disclosed (see Patent Document 1).
However, the radio communication system has been diversified recently, so the home agent cannot comprehend the information about a communication band capacity or a radio type being used by the mobile terminal with the method based on the care-of address of the mobile terminal.
Further, the QoS cannot be controlled so as to correspond to a band capacity which changes when the mobile terminal changes a destination of the radio connection (when handover is performed).
Thus, a mobile IP control system which can realize a seamless handover between different radio types of networks and control the QoS corresponding to the communication band used by the mobile terminal for the radio connection and the change therein has been demanded.    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-340982